The present inventions relate generally to mobile wireless communication devices, and more particularly to estimating Doppler spread/velocity in mobile wireless communication devices.
The performance of many cellular communication systems is dependent on the accuracy of the estimation of unknown parameters, for example, fading channel coefficients in third-generation cellular communication systems, by a mobile wireless communication station or device.
One significant source of parameter estimate inaccuracy is the Doppler phenomenon experienced when a mobile station is in motion. Channel estimation in some cellular communication systems, for example, requires filtering pilot signals received at the mobile station. The optimum bandwidth of the filter is dependent on the Doppler spread.
Velocity is proportional to frequency and thus to Doppler spread. Knowledge of accurate Doppler spread in mobile wireless communication devices is useful for assigning slower mobile stations to micro-cells and for assigning faster mobile stations to macro-cells, and for making relatively precise power control measurements.
It is known how to estimate Doppler spread based on the autocovariance of the square of the magnitude of a signal received at the mobile station. A problem with this approach however is estimator degradation, which results from poor noise immunity associated with estimating the autocovariance of a squared magnitude at lag 0. Another problem with this prior art approach is that it is based upon estimates of 1st and 2nd order moments of the squared magnitude of the received signal, which are basically 2nd and 4th order moments of the signal. Higher order moments of the received signal are generally more difficult to estimate than lower order moments thereof, and thus prior art Doppler spread estimates based on estimates of 1st and 2nd order moments of the squared magnitude of the received signal are susceptible to inaccuracies, which may result in poor system performance.
The various aspects, features and advantages of the present inventions will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description of the Inventions and the accompanying drawings described below.